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Now, the company says the FDA is requiring additional data as part of the submission, including results out to 168 weeks from a mid-stage study of 12 patients. The company reported data out to 144 weeks in July. The FDA is also looking for three-month data from at least 12 to 24 newly exposed patients by the time of submission, according to excerpts from FDA meeting minutes provided by the company.
"We are committed to satisfying the FDA's updated requests for these specific data to be included as part of an NDA (New Drug Application) submission and will continue to work with the agency toward the goal of a complete and acceptable NDA filing," Sarepta CEO Chris Garabedian said in a statement.
"We believe all of the data requests and additional FDA discussions that have currently been outlined can be completed in time for an NDA submission by mid-year 2015. Obtaining an FDA approval of eteplirsen for the DMD patients who may benefit from the drug continues to be our highest priority."
Duchenne muscular dystrophy affects about 1 in 3,500 boys born worldwide (DMD affects primarily boys because of the way it's inherited). It's caused by errors in the gene that codes for dystrophin, a protein important for muscle strength.
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Some of the FDA's questions, Sarepta said, center around the methods of measuring dystrophin; it also asked the company to acquire data from separate academic groups.
There are no drugs approved in the U.S. to treat DMD, and parent groups have become increasingly vocal about drug development. Parent Project Muscular Dystrophy, a non-profit focused on finding a cure for the disease, has urged the FDA to be flexible in its review of DMD drugs, given the progressiveness of the disease.
But development has been halting. Sarepta's eteplirsen is aimed at a subset of patients accounting for about 13 percent of boys with DMD. Another company, Prosensa, is also targeting that patient group with its drug, drisapersen. Prosensa said on Oct. 10 that it had begun the submission of its application for approval with the FDA on a rolling basis. The company began re-dosing patients in September from an earlier study; it, too, has had a rocky development timeline, as its late-stage study failed to show a statistically significant benefit and GlaxoSmithKline ended a partnership on the drug.
Today's delay for Sarepta potentially puts it several months behind Prosensa, changing the dynamics in a race thought to have the two companies on similar review timelines at the FDA.